The present invention relates to an internal combustion engine which is provided with a heat exchanger for cooling and/or preheating combustion air.
1. Field of the Invention
It is known to use combustion-air coolers (heat exchangers), according to which the cooling water of the internal combustion engine is utilized to cool the combustion air in the upper load range, and to heat up the combustion air in the lower load range (German Offenlegungsschrift No. 27 04 778).
2. Description of the Prior Art
Combustion-air coolers are also known according to which the atmospheric air is used to cool the combustion air (German Offenlegungsschrift No. 17 51 209). With such combustion-air coolers, it is furthermore known to take special measures for heating up the combustion air in the partial load range, for example heating up the combustion air using the exhaust gases of the internal combustion engine. The lubricating and transmission oils are also suitable media for preheating the combustion air in the partial load range.
The heretofore known combustion-air coolers primarily serve to provide the conditions for a higher power density of the internal combustion engine. This possibility is achieved in that the cooler combustion air effects a greater filling of the cylinder. Furthermore, cooling of the combustion air also has a favorable effect on the consumption of fuel and on the quality of the exhaust gas, especially on the generation of smoke, and is accompanied by a reduction of the thermal and mechanical stressing of the internal combustion engine and of all of the components which define the combustion chamber. This, for example at rapid changes of load, affects in particular the reduction of thermally alternating stresses. Furthermore, preheating the combustion air can favorably affect the white smoke tendency of the internal combustion engine.
For accomplishing this, it is naturally necessary to expend considerable expense, which consists in particular in that with liquid cooling an additional heat exchanger has to be provided, or the customary heat exchanger has to be enlarged; alternatively, when cooling with atmospheric air, cooling air has to be conveyed in an appropriate manner. In addition, certain standards have to be set with regard to the arrangement of such combustion-air coolers, which standards cannot always be readily fulfilled, since the overall size of such heat exchangers can be considerable. Furthermore, long air lines have an unfavorable effect on the performance of the internal combustion engine.
In a number of applications, cooling of the combustion air is only required for a very short period of time. This is true, for example, with the internal combustion engines of most passenger cars and light trucks in inner-city traffic. However, this is also true for internal combustion engines of excavators, in stacker trucks, and in other apparatuses. In such cases, it is therefore not even necessary to maintain cooling of the combustion air over longer periods of time, so that the measures can be limited to being effective for a short period of time. A similar situation exists for preheating during idling, to the extent that this is also limited to short time periods.
It is an object of the present invention to propose for supercharged internal combustion engines to have a combustion-air cooling system which is structurally simple to manufacture, and with which expensive measures in the form of special connections to the combustion-air cooling system for preheating the combustion air while maintaining a possibility for preheating can be extensively eliminated.